/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* reverse(ListNode* cur,ListNode* prev)
    {
        if(cur==nullptr)
        {
            return prev;
        }
        ListNode* ptr=cur->next;
        cur->next=prev;
        return reverse(ptr,cur);
    }
    ListNode* reverseList(ListNode* head) {
        ListNode* cur=head;
        ListNode* prev=nullptr;
        return reverse(cur,prev);
    }

};